Page 229 - Feline Cardiology

234 Section F: Arrhythmias and Other Electrocardiographic Abnormalities

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QRS
P

T

Figure 18.17. Ventricular tachycardia in a cat. A PVC (fifth beat from left; asterisk on inset; note shorter R-R interval than for the
first 4, sinus beats) initiates a monomorphic VT at a rate of 300 beats/minute. Macroreentry is less likely but cannot be ruled out.
25 mm/sec, 5 mm/mV.

because both simply represent different magnitudes of failure, may influence the choice of antiarrhythmics
Arrhythmias cific (unrelated to the arrhythmia; typically an asymp- moment (e.g., if centesis or diuretic administration
and even whether to withhold treatment for the
the same arrhythmia.
The chief complaint of cats with VT may be nonspe-
reestablishes normal oxygen delivery to the myocar-
dium and VT resolves).
tomatic heart murmur or incidental finding of
cardiomegaly on radiographs, for example), may suggest • Underlying triggers or potentiating factors that are
arrhythmia in an asymptomatic patient (e.g., irregular reversible—classically hypokalemia, anemia, hyper-
heart rhythm ausculted during a routine exam), or may thyroidism, and hypoxemia due to heart failure or
include overt clinical signs such as syncope as a result of severe airway disease—have all been sought with
tachycardia-associated reduced ventricular filling (see appropriate tests and corrected if present; often, cor-
Figure 18.1). Regardless of which of these three contexts rection of these abnormalities leads to resolution of
applies to a given case, the ECG is the diagnostic test of the arrhythmia without antiarrhythmic drugs.
choice. Extended monitoring (e.g., Holter or event
monitor) may be required to demonstrate VT in a Cats with VT that are showing overt clinical signs attrib-
patient where it is occurring intermittently, and the deci- utable only to the arrhythmia (i.e., syncope or collapse)
sion to proceed with such testing is dependent on the should be treated with antiarrhythmics, and the cat’s
owner’s opinion and desire, patient stability and risk to mentation, frequency and severity of such signs, and
the cat related to carrying the monitor, availability of the owner perception, desires, and financial considerations
monitoring equipment, and cost. should be included as determinants for whether to hos-
Antiarrhythmic options for addressing VT include pitalize for treatment and monitoring or to discharge
lidocaine, propranolol, esmolol, and magnesium sulfate and treat as an outpatient.
(IV) and procainamide, mexiletine, and sotalol (PO). Cats with VT that is not clearly responsible for clinical
Except in catastrophic clinical conditions (e.g., col- signs should be evaluated with portable ECG monitor-
lapsed, unconscious cat with ventricular tachycardia at ing. When this is not possible, such cats may be treated
340 beats/min), antiarrhythmic drugs should only be with antiarrhythmic drugs if the clinician keeps in mind
considered for a patient with VT once all of the follow- that treatment may in some cases worsen the patient’s
ing criteria have been met: status rather than improving it. Common examples of
pitfalls, and ways of avoiding them under these circum-
• The arrhythmia diagnosis is certain to be VT, not any stances, include
of its impostors (see Figures 18.14–18.16, 18.20a,
18.22, 18.24–18.27); misdiagnosis can lead to disas- • Judicious, not excessive, heart rate suppression. Typically
trous mistreatment as the “VT” fails to convert to a this is a concern with a beta blocker or a calcium-
normal rhythm and medication upon medication is channel blocker, and most often with intravenous use
administered with a growing but unjustified sense of but also possibly with oral use. A rapid change from
urgency. VT at 260 beats/minute, for example, to sinus rhythm
• An echocardiogram and thoracic radiographs have at 150 beats/minute, could be expected in some cats
been performed; the type of myocardial disease, if in response to beta-blockade if the dosage is high or
any, and presence or absence of congestive heart the cat is unusually sensitive to the drug. Such a drastic